OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 25 No. 3 2023 glass and carbon, natural fibers have many advantages. It can be stated that chemical composition and cell structure of natural fibers are quite complicated [6]. In addition to the advantages of using environmentally friendly materials, there are certain difficulties, such as relatively poor “matrix-fiber” interfacial adhesion when reinforcing and increased moisture absorption. Potential resource materials for various technical applications, including electrical, automotive, the packaging sector, and domestic use, include sisal, abaca, pineapple, agave, and banana fiber [7]. Polymer composites reinforced with synthetic fibers have excellent mechanical properties and lightweight construction [8]. The distribution of the fibers and the mechanical properties of the composite materials have been improved by treating the fibers with clay with an inorganic additive, although an additional mineral additive is probably needed in this area [9]. The automotive industry has recently become interested in natural fiber-based composite materials for a number of reasons, including improved vehicle fuel efficiency, and increased public concern over ecological sustainability. Natural fiber-reinforced composites are being used more and more in the construction and transportation sectors. Therefore, it is crucial to understand how it behaves in a fire [10]. Addition of rice bran into polylactic acid matrix (PLA) improves the mechanical properties and natural frequencies of rice bran PLA composite that can be used in 3D-printing [11]. The addition of short alpha fibers in epoxy makes composite more deformable and flexible due to lower stiffness values and high strain [12]. Based on the results of the analysis of free vibrations of the bamboo fiber composite, it is recommended for use in the transport and construction industries [13]. The surface treatment of natural fiber improves its mechanical and free vibration properties [14–17]. The free vibration values of flex fiber composite are dependent upon fiber direction and thickness [18]. The natural frequency of aloe vera fiber composite is affected by fiber stacking sequence, composite thickness and end conditions [19]. The natural frequency of composite beam increases with an increase in composite thickness regardless of boundary conditions. It also improves the modal damping of composite material [20, 21]. From the above literature, it can be concluded that the greatest amount of work has been done by researchers on the study of the mechanical properties of natural fibers composite materials; however, less attention has been paid to works related to the characteristics of free vibrations. In this paper, the mechanical properties of a polymer composite material based on Saccharum munja fibers were investigated along with its free vibration characteristics. Based on resonance peek in frequency response, the initial six-mode natural frequency with corresponding damping factors was obtained using an experimental setup. ANOVA analysis was performed to check the level of significance of the tensile and flexural tests. Research Methods Particulate (PC), short and random (SRC) and unidirectional (UDC) treated Saccharum munja fibers are considered as the reinforcing component of the composite material, while AW106 resin and an appropriate amount of HV953 hardener supplied by Prakash (Azamgarh, Uttar Pradesh, India) were used as matrix material. Saccharum Munya fibers were extracted from a dry plant obtained near the banks of the Gagara River (Gonda, Uttar Pradesh, India). Munya fibers were washed with 1 M NaOH solution for 30 minutes and then washed again in distilled water for 1 hour to remove traces of NaOH. Next, the washed fibers were dried in a hot cloth at 120 °C for 30 minutes. Washed again in distilled water and dried further in a hot cloth to remove any remaining NaOH and water content on the fiber surface. Compositions with different volumetric ratios used in this study are presented in Table 1. A compression molding machine (fig. 1) was used to form laminated composite materials (CM) with a size of 30×30×3 cm. First, a known amount of resin and hardener was poured into the mold cavity and waited for 90 minutes for solidification to begin. Then a mixture of resin and fiber was poured and again waited for 90 minutes. The mixture was compressed at a pressure of 120 bar and held at 800 °C for 48 hours. The processes of fabrication of Munja fiber composite laminates are presented in fig. 2. The fabricated laminates were cut in different shapes and sizes in accordance with ASTM standards for further analysis. ASTM D638 was used for tensile testing of rectangular fiber-polymer composite specimens with a gauge length of 57 mm. The test was carried out on a digital universal testing machine (UTM) manufactured by
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